Rapidly solidified Al3Ti-base alloys containing Ni

Abstract

Two Ni-modified Al₃Ti alloys (Al₆₅Ni₁₀Ti₂₅ and Al₆₂Ni₈Ti₃₀) were rapidly solidified by melt spinning. The resulting microstructure was studied using light microscopy and analytical electron microscopy. Significant variations in the microstructure and phases were observed between the two ribbons and through the thickness of each ribbon.A single-phase γ-TiAl structure was seen near the wheel side of the Al₆₂Ni₈Ti₃₀ ribbon, having microcrystalline grains ∼ 100 nm in diameter. Second-phase particles of Λ-AlNiTi were found in the remaining regions of that ribbon as the structure became columnar due to reduced rates of cooling. The Al₆₅Ni₁₀Ti₂₅ alloy exhibited a primary phase of π-Al_6.5 NiTi_2.5. A second phase of μ-Al₂NiTi formed with morphology and distribution varying through thickness. Microchemistry measurements on the phases indicated substantial deviations (up to 14 at. %) from the stoichiometric compositions. Further, the π, γ, and μ are low-temperature phases that do not form by solidification under equilibrium conditions. The observation of these phases thus suggests significant undercoolings achieved during the melt-spinning processing of the present alloys. Both ribbons are brittle as spun.